Cellulose lower alkanoate plastic composition



Patented Apr. 15, 1952 GELLULOSE LOWER ALKANOATE PLASTIC COMPOSITION Edward J. Wickson, South Orange, and Walter D. Paist, Berkley Heights, N. J., assignors to Cclanese Corporation of America, New York, N. Y., a corporation of Delaware N Drawing. Application December 16, 1949,

Serial No. 133,468 a 3 Claims. (01. ice-e177) I This invention relates to thermoplastic com positions and relates more particularly to fireretardant thermoplastic compositions having a basis'of cellulose acetate or other organic acid ester of cellulose.

An important object of this invention is the provision of fire-retardant thermoplastic compositions having a basis of cellulose acetate or other organic acid ester of cellulose which may be compounded without difficulty and which possess outstanding physical and chemical properties.

' Another object of this invention is the provision of fire-retardant thermoplastic compositions having a basis of cellulose acetate or other organic acid ester of cellulose plasticized with a mixture of tripropyl phosphate and triphenyl phosphate.

Other objects of this invention will be apparent from the following detailed description and claims. i

As is well known, fire-retardant thermoplastic compositions having a basis of cellulose acetate or other organic acid ester of cellulose may be prepared by incorporating a suitable plasticizer in said cellulose esters. While many of the plasticizers previously suggested for this purpose such as, for example, the trialkyl phosphates, produce thermoplastic compositions whose fire-retardant qualities are satisfactory, difficulties are often experienced in compounding these compositions and the physical and chemical properties of many of these thermoplastic compositions are deficient in one or more respects. Thus, certain of the previously suggested trialkyl phosphates, e. g. tributyl phosphate, liberate extremely irritating fumes when raised to elevated temperatures during the production and processing of thermoplastic compositions containing the same. Other trialkyl phosphates, such as triethyl phosphate, for example, yield thermoplastic compositions that have poor moisture resistance and heat stability, and in the presence of moisture, liberate materials that corrode carbon steel and chromium plated carbon steel. In addition, the mixing of thermoplastic compositions containing triethyl phosphate is difiicult, owing to the tendency thereof to form lumps and to the volatilization of an appreciable amount of the plasticizer during the working of the compositions on malaxating rolls. Tripropyl phosphate, when employed as the sole plasticizer, yields thermoplastic compositions that are free from some of the deficiencies specified above. However, such thermoplastic compositions containing tripropyl phosphate as the sole plasticizer have a low moisture resistance, poor dimensional stability and a high volatility on heating and, in addition, are difiicult to compound, owing to the high solvent power of the tripropyl phosphate for the cellulose esters.

According to the present invention, fire-retardant thermoplastic compositions having a basis of cellulose acetate .or other organic acid ester of cellulose and free from the deficiencies specified above are prepared by plasticizing said cellulose esters with a mixture of tripropyl phosphate and triphenyl phosphate. The fir'eI-retardant thermoplastic compositions of this invention may be mixed without difilculty since the plasticizers may be distributed uniformly throughout the cellulose esters without the formation of lumps, the liberation of irritating fumes, or the volatilization of any appreciable amount of the plasticizers during the workingof the compositions on'malaxating rolls. In addition, the fire-retardant thermoplastic compositions of this invention possess a very high impact strength, improved moisture resistanceand improved heat stability, and show less corrosive tendencies than compositions made with triethyl phosphate or triphenyl phosphate, or even mixtures of both. The fire-retardant thermoplastic compositions prepared in this manner are, therefore, eminently suited for a wide variety of applications. i

In preparing the fire-retardant thermoplastic compositions of this invention, from about 5 to 45% by weight of tripropyl phosphate basedon the weight of the cellulose ester and from about 5 to 30% by weight of triphenyl phosphate based on the weight of the cellulose ester are incorporated into the cellulose acetate or other organic acid ester of cellulose. The combined content of tripropyl phosphate and triphenyl phosphate should be suificient to yield a combined phosphate content, calculated as phosphoric acid, of at least about 6% by weight or preferably at least about 10% by weight based on the weight of the cellulose ester to impart the desired fire-retardant properties to the thermoplastic composition.

In addition to the plasticizers, the fire-retardant thermoplastic compositions of this invention may contain dyes, pigments, nacreous materials and other substances having a decorative effect. They may also contain stabilizers, ultraviolet light absorbing substances, and the like.

Where the novel fire-retardant thermoplastic compositions of this invention are to be employed as molding powders for the production of injection or compression moldings, or for extrupht . HQWIL sion operations, the molding powders may be prepared in a manner well known in the art.

For example, the cellulose ester may be mixed with the tripropyl phosphate in which is dissolved the triphenyl phosphate and passed repeatedly through the nip of heated malaxating rollsunt-il it is rendered homogeneous. The mixture is taken oh the malaxating rolls in the form of thin sheets, cooled and then broken into particlesoi a convenient size for use in molding and extrusion devices.

For the production of films and foils by the casting process, the cellulose ester, together with the desired amounts'of tripropyl phosphate and triphenyl phosphate, may be dissolved in a solvent or solvent mixture and the resulting solution deposited on a casting surface. Upon removal of the solvent or solvent mixture, the films or foils may be readily stripped irom the casting surface. ile-addition to cellulose acetate, other organic .ia id-cste s oi cel ulo et ma be mploye in ore a ins'the thermopl ic mp i n of th s-'in ention.;are, for e amp cellulose pro- ;niohat mel ulosebut rat cel u e e te-m pionate and cellulose acetateebutyrate.

..The followin examples are given'to illustrate 7 t is invention further.

Example I trio vr parts by weight of cellulose-acetate,

thereis addedzs parts by weight of'tripropyl phosphate having dissolved therein 205 parts fibyvlflght of, triphenyl phosphate. The mixture isloaded on. malaxating rolls maintained at a temperature of about 150 C. and rolled until it [is-homogeneous. During the mixing and rolling th re isvery' little. tendency towardlumping and abl irritating iumes-ereg ven off.

r Eccmnlcll J & ensemble of the mo d ng powder p pared in vL issuable]: ismolded intfoa bar. The bar'exits, Izod impact strength of 412 foot sounds/inch notc ;A parative contr bar co taining fo every 100 p t by'weight or cellupacetate. 4.6 parts "by weight of 'diethyl plateas the sole plasticizer exhibits an Izod impactstrength of only 3;? foot pounds/inch E amp 11.!

A Sample ofthe molding powder prepared in .E'xamplel is molded into a bar. The bar is held 'for:24 hours :at 100 F; and 1Q0% relative huemidity and then foran additionalr24q hours at 140 After vonesuch cycle the bar exhibits 'a-shrinkage of 0.1%. 'barexhibitsashrinkage of'0.2%. bar exhibits shrinkages of 0.2% and 0.4% after one. and'two cycles,-respec,tively.

After two such cycles the The control 7 Example IV ,A sample of the molding powder prepared in Example, I isdried for three hours at 100 to 110 6-. A aye of: the mo in powder about th ck is s read on thes rfa e o a a b steel *nla V 7 carbon steel plate.

sealed. jars-and held at a temperature of 125 and onth surf-ace of a chrom u plated The samples are placed in After. two we s. e e i n si n of. rrosio on the surface of either plate. A control made with 2,0,pa17ts by weight of triphenyl phosphate an -.2 a t by weishtoi trie p sphate for sistance.

. weight of triphenyl phosphate together with 100 4 7 each 100 parts by weight of "cellulose acetate tarnishes the carbon steel plate badly and strains the chromium plated carbon steel plate noticeably.

Example V V A molded bar is prepared in the manner set forth in Example II, employing 12 parts by weight "of triphenyl phosphate and 40 parts by weight of tripropyl phosphate for each 100 parts by weight of cellulose acetate. The bar exhibits an Izod impact strength of 5.4 foot pounds/inch notch. The bar also exhibits excellent firere- Example VI .A moldedbar is prepared in the manner set forth in 'Example'II, employing 10 parts by and 35 parts by weight of tripropyl phosphate parts by weight of cellulose propionate. The bar exhibits better dimensionalstabilitythananomparable. barplasticized withtripropyl phosphate as the sole piasticizer. The bar also exhibits better-fire resistance than a comparable bar plasticized with triphenyl phosphate-as the sole plasticizer.

It is to be understood that the foregoing-detailed description is given merely by way of illustration and that many variations may be made therein without departing vfrom the spirit of our invention. 7 p r V 7 Having described our invention, what we desire to secure by Letters Patentis:

1 A thermoplastic composition comprising a lower fatty acid ,ester-ofcellulose having incorporated thereina mixtureofirom about Etc by weight of tripropyl phosphate based onthe weight oi the cellulose ester-and from about ,5, to. 3.0% by weight of triphenyl phosphate basedon the weight of the cellulose ester, the combined Phosphate contentof the thermoplastic composition; calculated :as phosphoric .acid, being ;-at least about 10% by 'weightbasedon the weight of the cellulose ester.

.A thermoplastic composition comprising cellulose acetate having incorporated therein a 7 ,mixture oi ,from about 5 to 45% by weight of tripiopyl phosphate based on the weight of the cellulose acetate and from about 5 to 30% by weight of ftriphenyl phosphate based on the weight of the cellulose acetate, the combined phosphate content of thethermoplastic composition, calculated as phosphoric acid, being at REFERENCES CITED 7 The following references are of record in the file of this patent: UNITED STATES Pl'iTENTS Number Name Date 2,021,901 Smith Nov. 25, 1935 2,464,784

Easton Mar. 22, 1949 

1. A THERMOPLASTIC COMPOSITION COMPRISING A LOWER FATTY ACID ESTER OF CELLULOSE HAVING INCORPORATED THEREIN A MIXTURE OF FROM ABOUT 5 TO 45% BY WEIGHT OF TRIPROPYH PHOSPHATE BASED ON THE WEIGHT OF THE CELLULOSE ESTER AND FROM ABOUT 5 TO 30% BY WEIGHT OF TRIPHENYL PHOSPHATE BASED ON THE WEIGHT OF THE CELLULOSE ESTER, THE COMBINED PHOSPHATE CONTENT OF THE THERMOPLASTIC COMPOSITION, CALCULATED AS PHOSPHORIC ACID, BEING AT LEAST ABOUT 10% BY WEIGHT BASED ON THE WEIGHT OF THE CELLULOSE ESTER. 